n-th prime - n-th composite.

Terms

a(0) =-2a(1) =-3a(2) =-3a(3) =-2a(4) =1a(5) =1a(6) =3a(7) =4a(8) =7a(9) =11a(10) =11a(11) =16a(12) =19a(13) =19a(14) =22a(15) =27a(16) =32a(17) =33a(18) =37a(19) =39a(20) =40a(21) =45a(22) =48a(23) =53a(24) =59a(25) =62a(26) =63a(27) =65a(28) =65a(29) =68